1. Field of the Invention
This invention pertains to an automatic vertical storage and retrieval system and, more particularly, to a system having an extractor mechanism which is vertically stable and insensitive to changes in loading by means of one or more locking dogs.
2. Description of the Prior Art
Automatic vertical storage and retrieval systems are used to store various items in a vertical columnar array of storage platforms. Extractor mechanisms have been used in automatic vertical storage and retrieval systems such as in U.S. Pat. No. 5,544,996 for "Automated Storage and Retrieval System." These extractors allow items to be stored to and retrieved from the storage platforms.
Extractors of automatic vertical storage and retrieval systems typically travel vertically along and between the storage arrays by means of a chain or cable system driven by an electric motor. Optical encoders or similar means are used in automatic vertical storage and retrieval systems to position the extractor along the vertical array. An automatic vertical storage and retrieval system which uses an optical encoder at the motor to position the extractor must be periodically calibrated to account for drift in the calibration. The chain or cable drive system operates not only to drive and position the extractor mechanism but also to support the extractor mechanism while retrieving stored items or presenting retrieved items to the operator.
The chain or cable drive system in a typical automatic vertical storage and retrieval system may consist of a pair of chains or cables. One end of the each chain or cable is attached to opposite sides of the extractor, and the other end of each chain or cable is provided with a counterweight. The counterweight is used to compensate for the weight of the payload and to ease the strain on the motor drive during vertical displacement of the extractor. However, the extractor is vertically displaced in both a laden and an unladen condition and each payload differs in weight. Therefor, the effectiveness of counterweights in known automatic vertical storage and retrieval systems is limited. A payload weight of 500 pounds or more is not untypical in automatic vertical storage and retrieval systems. Because of the weight of such payloads, a danger of chain or cable breakage exists in known vertical storage and retrieval systems. Even if the chain or cable does not break, any stretching of the chain, cable or support members, even if slight, could cause a misalignment problem.
Therefore, in order to alleviate these problems, an objective of the present invention is to provide an automatic vertical storage and retrieval system with an extractor mechanism which is vertically stable at all four corners. Another objective of the present invention is to provide an automatic vertical storage and retrieval system with a positive positioning system which does not rely on an optical encoder to maintain precise vertical positioning or for final vertical positioning. Another objective of the present invention is to provide an automatic vertical storage and retrieval system with an extractor mechanism which is supported by one or more locking dogs during retrieval of stored items and presentation of retrieved items to the operator, thereby causing the extractor to maintain a horizontal attitude regardless of uneven or off-center loading. Yet another objective of the present invention is to provide an automatic vertical storage and retrieval system with an extractor mechanism which is supported by the locking dogs whenever the extractor is in a rest position to increase safety toward person's servicing, operating and maintaining the vertical storage and retrieval system.